To ensure safety to patients, dental materials must be tested for biocompatibility before they can be used clinically. The objective of this research plan is to determine whether the human cloning assay (HTCA), a two-layer soft agar system can be used to evaluate the cytotoxicity of various alloys used in crowns and bridges. Because the assay measures cell proliferation it has the potential of recognizing cell damage which might not be detected by other in vitro tests. This assay will be used to determine whether P3J and T24, two human tumor cell lines can form colonies in the presence of various dental alloys. Preliminary results have shown that with P3J, the assay allowed us to determine the concentration at which various metals (used in dental alloys) prevented colony formation. The results observed using this assay with dental alloys will be compared to those obtained using two in vitro tests (and cell lines) currently used by others to evaluate dental materials. These tests, the direct contact method and the agar diffusion method consist of scoring the damage to cells (in monolayers) following a 24-hour exposure to alloys. The cell lines to be used in these tests will include WI-38, a diploid cell line from normal lung; Vero, a fibroblast-like cell from monkey kidney tissue and T24 which also grows as a monolayer in liquid culture.